Linux内核如何处理并发文件查找

Question

假设同时有两个进程looking up一个文件，并且此文件在dcache中尚不存在。这两个查找将向进程返回NULL（dentry）。

我的问题是Linux内核如何确保在dentry查找失败后，它只创建一个dentry？

Answer 1

1912 /**
1913  * d_lookup - search for a dentry
1914  * @parent: parent dentry
1915  * @name: qstr of name we wish to find
1916  * Returns: dentry, or NULL
1917  *
1918  * d_lookup searches the children of the parent dentry for the name in
1919  * question. If the dentry is found its reference count is incremented and the
1920  * dentry is returned. The caller must use dput to free the entry when it has
1921  * finished using it. %NULL is returned if the dentry does not exist.
1922  */

d_lookup不会自己创建任何dentry个对象。查看do_filp_open逻辑，它会显示dentries的创建方式。